Determine which Java compiler was used for compilation

I have an existing Java web application running on Tomcat. The class files are arranged in folders and I was trying to build the structure into a JBuilder 9 personal project file, but I am not having much luck. I have maintained another existing java project in JBuilder and it worked fine. I don't know what compiler was used to create the class files for the second project.

1. Is there any way to determine which compiler was used by looking at the class files? I tried looking through the files with a text editor, but I did not see anything useful.

2. If I don't have the existing project definition anyway, which development tool should I use and how do I setup the project?

The caveat is the original developer is no longer available so I don't have the ability to get the information from him. I am a long time developer, just a little new to the java environments. If anyone can point me in the right direction, I should be able to take it from there.